Adjustable ball lead nut

ABSTRACT

In combination, an adjustable ball lead nut and a ball lead screw having complementary channels or grooves cooperating to define a helical duct, an adjustment disc mounted at one end of the nut and adapted to rotate with respect thereto over a limited angle, the lead nut and adjustment disc being provided with complementary channels or grooves cooperating to define an adjustment loop duct being in series with the helical duct, and a plurality of ball bearings disposed within the ducts, rotation of the adjustment disc in one direction causing the adjustment loop duct to decrease in length, thereby bringing the ball bearings into mutual engagement and providing compensation for wear of said ball bearings. Additional structure is provided to facilitate the movement of ball bearings through the various ducts.

Helmer [451 Feb. 12, 1974 ADJUSTABLE BALL LEAD NUT [76] Inventor: JesseNorman Helmer, Rt. 1, Box

Related US. Application Data [63] Continuation-impart of Ser. No.157,377, June 28,

1971, abandoned.

[52] U.S. Cl 74/459, 74/424.8, 74/441 [51] Int. Cl. F16h 55/28, Fl6h55/18 [58] Field of Search 74/441, 459, 424.8, 89.15

[5 6] References Cited UNITED STATES PATENTS 5/1966 Ziver 74/424.8 R2/1965 Bohnhoff 74/424.8 R

Primary Examiner-Charles J. Myhre Assistant ExaminerFrank H. McKenzie,Jr.

[ ABSTRACT In combination, an adjustable ball lead nut and a ball leadscrew having complementary channels or grooves cooperating to define ahelical duct, an adjustment disc mounted at one end of the nut andadapted to rotate with respect thereto over a limited angle, the leadnut and adjustment disc being provided with complementary channels orgrooves cooperating to define an adjustment loop duct being in serieswith the helical duct, and a plurality of ball bearings disposed withinthe ducts, rotation of the adjustment disc in one direction causing theadjustment loop duct to decrease in length, thereby bringing the ballbearings into mutual engagement and providing compensation for wear ofsaid ball bearings. Additional structure is provided to facilitate themovement of ball bearings through the various ducts.

12 Claims, 12 Drawing Figures mgmmrmzmm I 3 791 282 sum 1 or a figure 2PATENTED FEB 1 2 1974 3791232 sum 2 or 3 PATENTEOFEBWSM 3 791 232 sum 3or 3 I f/ are 9 4% g 1 ADJUSTABLE BALL LEAD NUT BACKGROUND OF THEINVENTION This application is a continuationin-part of pendingapplication Ser. No. 157,377, filed June 28, 1971 now abandoned by JesseNorman Helmer.

FIELDFOF INVENTION The present invention relates to machine lead screwand nut apparatus, and is more particularly concerned with a machinelead screw and nut combination provided with complementary channels orgrooves defining a helical duct and having a plurality of ball bearingsdisposed within the duct.

PRIOR ART Apparatus of the type described is generally known in the art.The use of ball bearings to provide engagement between a nut and a leadscrew provides a positive engagement'with low friction. However, suchapparatus has the disadvantage that when the ball bearings wear theybecome smaller and considerable back lash or sloppiness develops in theengagement between the lead screw and nut. Some attempts have been madeto remedy the situation. For example, U. S. Pat. No. 3,053,105 disclosesa means for compensating against wear of such devices utilizing aresilient disc or annulus. Further, in U. S. Pat. No. 3,141,349 attemptsare made to compensate for wear by utilizing a twomember nut having anelastomeric inner face, the two members being compressible together totake up slack caused by ball bearing wear. Such compensation means havenot proved to be entirely satisfactory, since in one case positivelinear force maintaining the ball bearings in place is not achieved, andin the other case the grooves of the nut and lead screw are offset,causing undue wear on one side of each channel.

OBJECTS OF THE INVENTION It is an object of the invention to provide alead screw and nut combination utilizing ball bearings for providing lowfriction engagement of the nut and lead screw. It is a further object toprovide an apparatus of the type described having novel means forcompensating for ball bearing wear. It is an additional object toprovide such an apparatus having means provided for facilitatingmovement of the ball bearings along the various ducts. It is still afurther object to provide a structure which is more easily machined andassembled than prior art structures.

According to the invention, a lead screw and nut combination is providedutilizing ball bearings for engagement, and having an adjustment discrotatably mounted on the nut, the adjustment disc having ducts providedtherein to provide an adjustable loop duct of ball hearings in serieswith the main duct of ball bearings which increases or decreases inlength as the disc is rotated in one direction or the other. Rotation ofthe disc in direction of decreasing length causes the adjustment loop toshorten until the ball bearings throughout the apparatus engage eachother closely, thereby compensating for wear. Additional structure inthe form of tangentially oriented ducts and cooperating bosses toimprove the operation of the apparatus, and discontinuous annular ductsto facilitate fabrication of the apparatus are also provided.

BRIEF DESCRIPTION OF THE DRAWING In the drawings,

FIG. I is a sectional view of one embodiment of the ball lead screw andnut combination of the invention, taken at the line I-I of FIG. 3,looking in the direction of the arrows.

FIG. 2 is a cross-sectional view taken at the line IIII of FIG. 1,looking in the direction of the arrows.

FIG. 3 is a cross-sectional view taken at the line III- III of FIG. 1,looking in the direction of the arrows.

FIG. 4 is a sectional view of another embodiment of the invention.

FIG. 5 is a cross-sectional view taken at the line V--V of FIG. 4,looking in the direction of the arrows.

FIG. 6 is a cross-sectional view taken at the line VIVI of FIG. 4,looking in the direction of the arrows.

FIG. 7 is a cross-sectional view taken at the line VII- VII of FIG. 4,looking in the direction of the arrows.

FIG. 8 is a cross-sectional view taken at the line VIII- -VIII of FIG.4, looking in the direction of the arrows.

FIG. 9 is a top view partly broken away and partly in cross-section ofthe device shown in FIGS. 4-8, and illustrating the apparatus with theadjustment disc in one rotative position.

FIG. 10 is a top view of the apparatus, partly broken away and partly incross-section of the apparatus shown in FIGS. 4-8 and illustrating theadjustment disc in another rotative position.

FIG. 11 is a diagrammatic perspective view showing the general outlineof the apparatus in broken lines, and showing the configuration of theball bearingcontaining channels, and

FIG. 12 is a cross-sectional view taken at the line XII- -XII of FIG. 4,looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-3, a ballnut and lead screw assembly 10 is shown comprising a lead screw 11 and acylindrically shaped lead nut 12. The surface of the lead screw 11 isprovided with a helical channel or groove 13 and the lead nut 12 isprovided with a complementary helical channel or groove 14. The helicalchannels 13 and 14 cooperate to define a helical duct 15 adapted toreceive a plurality of ball bearings 16. The nut 12 is provided with aflange 17. An annular adjustment disc 18 is rotatively mounted on anaxial extension 12a of the nut 12 and against the face of the flange 17by means of bolts 19 extending through arcuate slots 20 provided in theadjustment disc, and threadedly engaged in the flange. The adjustmentdisc 18 is adapted to be rotated through an arc defined by the length ofthe arcuate slots 20, and to remain fixed at any desired rotativeposition when the bolts 19 are tightened.

At the remote end of the lead nut 12 the helical duct 15 is connected toa longitudinal transfer duct 21 which is connected at its other end to adiscontinuous annular channel 22 coaxially positioned with respect toand provided in the face surface of the nut 12, and having one endconnected to the duct 21, which channel cooperates with the face of theadjustment disc 18 to define an annular duct 22a. An arcuate detent 30extends axially from the adjustment disc 18 and rides in the channe122to provide an adjustable limit defining the length of the adjustableduct 22a. A lip 31 is provided for funnelling ball bearings 16 into anaperture 23 in the adjustment disc 18 which leads to a transverse duct230. A discontinuous annular channel 24 is provided on the inner axialsurface of the adjustment disc 18 which cooperates with the surface ofthe axial extension 12a to define an annular duct 24a connected at oneend to the transverse duct 23a and at the other end to a connecting duct25 which in turn is connected to the main helical duct 15, andjuxtaposed with respect to the annular duct 22a. The channels and ductswithin the lead nut 12 and adjustment disc 18 cooperate to form anadjustable loop duct whose length may be varied by rotating theadjustment disc 18, as will be explained in greater detail below.

In operation, all the ducts are filled with ball bearings until theapparatus is completely filled. A ball bearing filling hole 26 isprovided for introducing ball bearings into the ducts and maintainedclosed by a screw 27. The adjustment disc 18 is then rotated until theball bearings 16 snugly engage each other. As the lead screw is turnedwith respect to the lead nut, the ball bearings leave the main helicalduct at one end and enter at the other end. They continue to passthrough all the ducts which are arranged in series, the longitudinaltransfer duct, the adjustable loop duct, and back through the connectingduct to the other end of the main helical duct. When the screw is turnedin an opposite direction, the direction of motion of the ball bearingsis reversed. However, the ball bearings continue in engagement with eachother. When wear takes place and the ball bearings no longer engage eachother, the adjustment disc is further rotated to shorten the adjustmentloop duct and to place the ball bearings once again in engagement witheach other. A dowel pin or screw 28 is provided at each end of the nutto guide the ball bearings into or out of the longitudinal transfer duct21 at one end and into or out of the connecting duct 25 at the other endfrom the main channel. Additional threaded holes 29 are provided formounting the adjustment disc in different rotative position ranges.

Referring to FIGS. 4-12, a somewhat modified form of the invention isillustrated comprising a lead nut and lead screw assembly 36 having alead screw 37, a cylindrical lead nut 38 having annular axial extensions39 and 40. The lead screw 37 is provided with a helical channel 41 andthe lead nut 38 is provided with a complementary helical channel 42cooperating with the helical channel 41 to define a helical ball bearingmain duct 43. As can be seen in FIG. 4, the channel 42 provided in thelead nut is deeper than the channel 41 provided in the lead screw. As aresult, the ball bearings more readily roll into the connecting ducts ofthe lead nut to be described.

An adjustment disc 44 is rotatably mounted at one end of the lead nut 38on the axial extension 39 and is maintained thereon by means of bolts 45positioned in arcuate slots 46 provided in the adjustment disc 44 andthreadedly engaged in apertures provided at the periphery of the face ofthe lead nut 38. The adjustment disc 44 is rotatable with respect to thelead nut through an are defined by the length of the arcuate slots 46.

An annular disc 47 is mounted at the other end of the nut 38 over theaxial extension 40 and is affixed to the nut by means of bolts 48mounted through apertures provided in the disc and threadedly engaged inthreaded holes provided in the nut.

As shown in FIG. 4, in order to limit the travel of the ball bearings atthe ends of the helical duct 43, the axial extension 39 is recessed topermit a limiting ring 49 to be positioned therein and retained by meansof pins or dowels 50 placed through apertures in the axial extension 39and engaging grooves provided in the limiting ring 49. Similarly, theaxial extension 40 is recessed to receive a limiting ring 51 which issimilarly maintained in place by pins or dowels 52.

As shown in FIG. 4, a longitudinal transfer duct 53 is utilized totransfer ball bearings 54 from one end of the helical duct 43 to theother. The ball bearings are transferred from the end of the transferduct 53 adjacent the annular disc 47 to the helical duct 43 by means ofa connecting duct system provided in the annular disc 47. As shown inFIGS. 4 and 7, the annular disc is provided with a discontinuous annularchannel 56 provided on the axial inner surface of the disc, andcooperating with the outer surface of the axial extension 40 to define adiscontinuous annular duct 57. The axial extension 40 is provided with aradially extending boss 58 slidably positioned within the annular duct57. At the leading edge 59 of the boss 58 is a duct 60 connected at oneend to the annular duct 57 and at the other end entering the helicalduct 43 tangentially. At the upper end of the duct 57 is an elbow duct61 connecting the duct to the longitudinal transfer duct 53.

As shown in FIGS. 4 and 8, the longitudinal transfer duct 53 isconnected at one end to a discontinuous annular channel 62 provided inthe face of the lead nut 38 which cooperates with the face of theadjustment disc 44 to provide a discontinuous annular duct 63 connectedat one end to the end of the transfer duct 53. An arcuate detent 65extends axially from the adjustment disc 44 and rides in the channel 62,providing an adjustable limit for the other end of the duct 63.

As shown particularly in FIGS. 9 and 10, the adjustment disc 44 is alsoprovided with a discontinuous annular channel 66 at its inner axialsurface which cooperates with the outer surface of the axial extension39 to provide a discontinuous annular duct 67 similar to the annularduct 57 provided in the annular disc 47. As shown in FIG. 12, thearcuate detent 65 is provided with a lip 68 which guides ball bearings54 from the annular duct 63 to a U-form transverse duct 69 (shown indetail in FIGS. 9 and 10), and into the annular duct 67. The axialextension 39 is provided with an arcuate boss 70 which extends into andrides in the annular channel 67 thereby defining one end of the annularduct 67. As shown in FIGS. 5 and 6, at the leading edge 71 of the boss70 a duct 72 is connected to the channel 67 and extends tangentially toand connects with the helical duct 43 at one end thereof.

A recess 73 is provided in the adjustment disc 44 to permit the boss 70to enter and engage the annular channel 66 when the adjustment disc isassembled onto the nut. A similar recess may be provided in the annulardisc 47 to permit the boss 58 to enter the annular channel 56 forassembly.

FIG. 1 1 illustrates the spacial arrangement of the ball bearing ducts.As the lead screw 37 is turned with respect to the lead nut 38, the ballbearings 54 leave the main helical duct 43 at one end and enter at theother. When the nut is turned in one direction, for example, the ballbearings at the remote end of the nut travel through the tangential duct60 into the transfer duct 53 where they proceed until they enter theannular duct 67, continue through the transverse duct 69 and into theannular duct 67 provided in the adjustment disc 44. They then are guidedby the boss 70 into the tangential duct 72 and back into the helicalduct 43.

FIGS. 9 and 10 illustrate the principle of operation of 5 the presentinvention. During operation, wear isencounteredwith respect to the ballbearings and even the channel in which they are disposed between the nutand lead screw. As a result the ball bearings do not touch each otherand there may be considerable play or backlash between the nut and thelead screw. According to the invention such wear is compensated for byrotating the adjustment disc 44 and shortening the adjustable loop ductformed by ducts 63, 69, and 67 and thereby the overall length of theduct in which the ball bearings travel, thereby placing the ballbearings in close engagement with each other.

Referring to FIG. 10, a position of the adjustment disc with respect tothe nut'is shown in which the adjustment loop duct formed by cooperationby the ducts of the adjustment disc and nut is long. This is theposition before initial adjustment is made or before adjustment is madeto compensate for wear. To provide such compensation the adjustment discis rotated in a direction to shortenthe loop duct and until the ballbearings closely engage each other. Such a position is shown in FIG. 9.The bolts 45 are then tightened. After further use and further wear, theadjustment disc may be once again rotated to shorten the loop stillfurther, thereby shortening the overall length of the ball bearing ductuntil all the ball bearings are again in close engagement. To facilitaterotation of the adjustment disc, spanner wrench notches 74 may beprovided as shown in FIGS. 5 and 6.

The apparatus is assembled by placing the lead nut over the lead screw,and with either the adjustment disc 44 or annular disc 47 in place. Theducts are then completely filled with ball bearings. The remaining discis then mounted by placing the boss of the respective axial extensionthrough the recess 73, and rotating the respective disc to engage theboss in the respective annular channel. The disc is then affixed to thenut by means of bolts. The length of the adjustment loop is then reduceduntil all the ball bearings are in close engagement, the bolt then beingtightened in place.

The adjustable lead screw and nut apparatus according to the presentinvention has several advantages over prior art lead screw and nutapparatus utilizing ball bearings. The primary advantage is that theapparatus provides a very quick and effective adjustment for wear byrotation of the adjustment disc. Because of the nature of thearrangement, a substantial shortening of the overall ball bearing ductmay be accomplished which can compensate for a large degree of wear. Inprior art arrangements, only small amounts of wear could be compensatedfor. Further, the present apparatus provides a more positive adjustmentbecause the ball bearings are maintained in steel-to-steel adjustment,thereby obviating the sloppiness or backlash which might be introducedby utilizing resilient discs to take up the slack space when ballbearing wear is encountered. Further, the apparatus can be effectivelyand accurately operated over long periods of time without the necessityfor disassembly.

A further advantage of the invention is provided by the structure inwhich the adjustment disc 44 and the annular disc 47 are both separatestructures. This permits the transfer ducts and adjustment ducts to beeasily provided by machining the annular structures. The use of anarcuate boss cooperating with a tangential duct for feeding or unloadingball bearings with respect to the axial duct facilitates their transferback and forth and prevents the jamming up of ball bearings whichresults when normally directed ducts are utilized. Moreover, thetangential edge of the boss facilitates feeding ball bearings into thelongitudinal transfer duct at one end and into the annular duct 63 atthe other. Further improvements in structure result from the use of thelimiting rings which are recessed within the axial extensions, therebyfacilitating the machining of the structure and providing a readilyadjustable limit for forcing ball bearings out of the axial duct andinto the tangential ducts.

It is to be understood that the invention is not to be limited to theexact details of structure and operation shown and described, as obviousmodifications and equivalents will be apparent to one skilled in theart.

I claim:

1. In combination, an adjustable ball lead nut and a ball lead screwhaving complementary helically arranged grooves cooperating to define ahelical ball bearing duct, an adjustment member rotatably mounted at oneend of said nut, a return duct connecting one end of said helical ductwith the other, and adapted to have a plurality of ball bearingsdisposed in said helical duct and said return duct, portions of saidreturn duct being disposed in said adjustment member and the adjacentend of said nut, said portions cooperating to define an adjustable loopduct and being so disposed that rotation of said adjustment member inone direction shortens said adjustment loop and causes said ballbearings to become positioned in close mutual engagement, therebycompensating for wear.

2. The combination according to claim 1, wherein said adjustable loopduct comprises an annular channel provided in one end of said nutcooperating with a surface of said adjustment member to define a firstdiscontinuous annular duct, a transverse duct provided in saidadjustment member and communicating at one end with said first annularduct, and a second discontinuous annular duct provided in saidadjustment member connected at one end with said transverse duct, saidsecond annular duct being juxtaposed with respect to said first annularduct, the other end of said second annular duct being connected to aconnecting duct which in turn is connected to one end of said helicalduct.

3. The combination according to claim 2, wherein said return ductincludes a longitudinally disposed duct communicating at one end withthe remote end of said helical duct and communicating at the other endwith said first annular duct.

4. The combination according to claim ll, wherein said lead nut isprovided with a filling duct communicating with said helical duct forfilling said helical duct with ball bearings, and having means providedfor closing said filling duct to prevent ball bearings from escapingthrough said filling duct during operation.

5. The combination according to claim 1, wherein an angularly positionedboss is provided at each end of said lead nut positioned to guide ballbearings leaving and entering said helical duct in a continuous stream.

6. The combination according to claim 1, wherein said adjustment memberis disc-form and mounted on said lead nut by means of screws extendingthrough arcuate slots provided in said adjustment member and threadedlyengaged in said lead nut.

7. The combination according to claim 6, wherein the inner face of saidadjustment member is provided with an arcuate detent extending axiallyinto the annular channel provided in one end of said nut and serving asan adjustable limit for said first annular duct, and said detent isprovided at one end with a lip for guiding ball bearings into saidtransverse duct.

8. The combination according to claim 7, wherein said lead nut isprovided with axial extensions wherein said adjustment member isrotatably mounted on an axial extension at one end, and having at theother end an annular disc rotatably mounted on the other of said axialextensions, the inner axial surface of said annular disc being providedwith a discontinuous annular channel cooperating with the surface ofsaid axial extension to define a discontinuous annular duct, said axialextension having an arcuate boss extending radially into said annularchannel and providing a limit for said annular duct, a duct provided insaid axial extension having an opening adjacent one end of said bosscommunicating with said annular duct and being tangentially positionedwith respect to and communicating with one end of said helical duct, andduct means connecting said discontinuous annular duct with saidlongitudinally disposed duct.

9. The combination according to claim 7, wherein said second annularduct comprises a discontinuous annular channel provided on the inneraxial surface of said adjustment member cooperating with the outersurface of the axial extension on which said adjustment member isrotatably mounted, said axial extension being provided with an arcuateboss extending radially into and riding in said annular channel, andproviding a limit for said channel, and a duct having an orificeimmediately adjacent to one end of said boss and extending in said axialextension tangentially to and communicating with one end of said helicalduct.

10. The combination according to claim 7, wherein said axial extensionsare recessed to receive limiting rings mounted therein to provide limitsfor said helical duct, and preventing said ball bearings from leavingsaid lead nut during operation.

11. The combination according to claim 1, wherein the helically arrangedgrooves provided in said lead nut are deeper than the helically arrangedgrooves provided in said lead screw,

12. In combination, an adjustment ball lead nut and a ball lead screwhaving complementary helically arranged grooves cooperating to define ahelical ball bearing duct, a longitudinal transfer duct for transferringball bearings from one end of said helical duct to the other when saidlead screw is rotated with respect to said lead nut, and means forconnecting an end of said helical duct to said longitudinal transferduct, comprising an axial extension provided at an end of said lead nut,an annular disc rotatably mounted on said axial extension having meansfor being affixed to said nut, the annular disc having a discontinuousannular channel provided at its inner axial surface cooperating with thesurface of said extension to define a discontinuous annular duct, saidaxial extension having an arcuate boss extending radially into saidannular channel and providing a limit for said duct, a duct provided insaid annular axial extension having an opening adjacent one end of saidboss communicating with said annular duct and being tangentiallypositioned with respect to and communicating with one end of saidhelical duct, and duct means connecting said discontinuous annular ductwith said longitudinally disposed duct.

1. In combination, an adjustable ball lead nut and a ball lead screwhaving complementary helically arranged grooves cooperating to define ahelical ball bearing duct, an adjustment member rotatably mounted at oneend of said nut, a return duct connecting one end of said helical ductwith the other, and adapted to have a plurality of ball bearingsdisposed in said helical duct and said return duct, portions of saidreturn duct being disposed in said adjustment member and the adjacentend of said nut, said portions cooperating to define an adjustable loopduCt and being so disposed that rotation of said adjustment member inone direction shortens said adjustment loop and causes said ballbearings to become positioned in close mutual engagement, therebycompensating for wear.
 2. The combination according to claim 1, whereinsaid adjustable loop duct comprises an annular channel provided in oneend of said nut cooperating with a surface of said adjustment member todefine a first discontinuous annular duct, a transverse duct provided insaid adjustment member and communicating at one end with said firstannular duct, and a second discontinuous annular duct provided in saidadjustment member connected at one end with said transverse duct, saidsecond annular duct being juxtaposed with respect to said first annularduct, the other end of said second annular duct being connected to aconnecting duct which in turn is connected to one end of said helicalduct.
 3. The combination according to claim 2, wherein said return ductincludes a longitudinally disposed duct communicating at one end withthe remote end of said helical duct and communicating at the other endwith said first annular duct.
 4. The combination according to claim 1,wherein said lead nut is provided with a filling duct communicating withsaid helical duct for filling said helical duct with ball bearings, andhaving means provided for closing said filling duct to prevent ballbearings from escaping through said filling duct during operation. 5.The combination according to claim 1, wherein an angularly positionedboss is provided at each end of said lead nut positioned to guide ballbearings leaving and entering said helical duct in a continuous stream.6. The combination according to claim 1, wherein said adjustment memberis disc-form and mounted on said lead nut by means of screws extendingthrough arcuate slots provided in said adjustment member and threadedlyengaged in said lead nut.
 7. The combination according to claim 6,wherein the inner face of said adjustment member is provided with anarcuate detent extending axially into the annular channel provided inone end of said nut and serving as an adjustable limit for said firstannular duct, and said detent is provided at one end with a lip forguiding ball bearings into said transverse duct.
 8. The combinationaccording to claim 7, wherein said lead nut is provided with axialextensions wherein said adjustment member is rotatably mounted on anaxial extension at one end, and having at the other end an annular discrotatably mounted on the other of said axial extensions, the inner axialsurface of said annular disc being provided with a discontinuous annularchannel cooperating with the surface of said axial extension to define adiscontinuous annular duct, said axial extension having an arcuate bossextending radially into said annular channel and providing a limit forsaid annular duct, a duct provided in said axial extension having anopening adjacent one end of said boss communicating with said annularduct and being tangentially positioned with respect to and communicatingwith one end of said helical duct, and duct means connecting saiddiscontinuous annular duct with said longitudinally disposed duct. 9.The combination according to claim 7, wherein said second annular ductcomprises a discontinuous annular channel provided on the inner axialsurface of said adjustment member cooperating with the outer surface ofthe axial extension on which said adjustment member is rotatablymounted, said axial extension being provided with an arcuate bossextending radially into and riding in said annular channel, andproviding a limit for said channel, and a duct having an orificeimmediately adjacent to one end of said boss and extending in said axialextension tangentially to and communicating with one end of said helicalduct.
 10. The combination according to claim 7, wherein said axialextensions are recessed to receive limiting rings mounted therein toprovide limits for said helical duct, and preventing said ball bearingsfrom leaving said lead nut during operation.
 11. The combinationaccording to claim 1, wherein the helically arranged grooves provided insaid lead nut are deeper than the helically arranged grooves provided insaid lead screw.
 12. In combination, an adjustment ball lead nut and aball lead screw having complementary helically arranged groovescooperating to define a helical ball bearing duct, a longitudinaltransfer duct for transferring ball bearings from one end of saidhelical duct to the other when said lead screw is rotated with respectto said lead nut, and means for connecting an end of said helical ductto said longitudinal transfer duct, comprising an axial extensionprovided at an end of said lead nut, an annular disc rotatably mountedon said axial extension having means for being affixed to said nut, theannular disc having a discontinuous annular channel provided at itsinner axial surface cooperating with the surface of said extension todefine a discontinuous annular duct, said axial extension having anarcuate boss extending radially into said annular channel and providinga limit for said duct, a duct provided in said annular axial extensionhaving an opening adjacent one end of said boss communicating with saidannular duct and being tangentially positioned with respect to andcommunicating with one end of said helical duct, and duct meansconnecting said discontinuous annular duct with said longitudinallydisposed duct.